Inductive proximity sensors have been used for many applications requiring motion detection. Proximity sensors come in various shapes and sizes. Some are tubular while others rectangle and pancake style. It is to be noted that the foregoing sensor applications are tubular in design. These sensors, when a metal object is passed over their sensing face, will turn on or off, depending on the configuration of the sensor. The configuration of the sensor can be a normally open or normally closed. An example would be that if voltage is applied to a normally open sensor and there is not a metal target over the face then the output of the sensor would be zero. Accordingly, when metal is passed over the face, the output would be the same as the voltage it is being powered with. Further, a normally closed sensor output would be the same as its input with no metal at the face and zero when metal is passed over the face. Most of industry relies on these proximity sensors to detect motion on equipment. Some of this equipment has rotating shafts, gates that open and close and many other examples. The end result from using sensors is to provide either signal (as in the case of a normally closed or normally open sensor configuration) that can be sent to a computer, indicator light, alarm or many other devices that can show if equipment being monitored is preforming correctly.
The proximity sensor needs a metal target passed over the sensing face to become active. There are many ways to install sensors and to install metal targets for the sensor to detect. On rotating shafts of equipment, metal targets have been welded or attached with threaded holes. On non-rotating equipment, such as a two part gate, steel has been welded on one half of the gate and the sensor mounted on the other so as the gate closed, the sensor would detect the welded steel target. Further, as the gate opened and the two half's of the clam opened, the sensor would lose presence of the welded target and lose detection. In any case, the above examples are just a representative of possible ways target metal and sensors can be mounted. It is just an example which are used but not deemed the only way to mount such devices and how they are used to detect movement of an apparatus.
Proximity sensors have to be mounted and positioned according to their detection distance and position. Whereas, if a sensor had a sensing distance of 0.125 inches, it has to be mounted within 0.125 inches from the metal target to operate correctly. Also, the sensor sensing face has to be in line with the target. On a tubular sensor, the face is at one end of the tubular configuration. Obviously, if the target metal exceeds the maximum detection distance, the proximity sensor will not detect the target and thus not operate. End users of these sensors are limited in how they and the target metal are mounted. The manufacturers of sensors provide many accessories that secure the sensors when mounted so as to secure any movement of the sensor. They also provide target metal which also has to be secured. In any case, it is still the end user's responsibility to mount both the sensor and the target within the parameters of sensing distance. The mounting varies according to the characteristics of the apparatus that is being monitored for movement. One example would be a rotating shaft. The target would have to be attached to the shaft and the sensor mounted nearby within the detection range. A simple explanation of this process can be explained by using a common door that opens and closes. If the sensor is mounted on the door frame and the target mounted on the door it should be obvious that when the door is closed the sensor detect the target and turns on. When the door is opened the sensor loses detection of target and turns off. In any case, the detection distance must be obtained for proper operation.
End users of proximity sensors are limited in mounting possibilities because of the small detection distance. In simpler examples such as a door, it would not be too difficult to stay within the detection distance parameters. In other cases, such as a rotating shaft on equipment, the mounting becomes more difficult. The majority of sensor use in industry is such that difficulties arise when trying to mount sensor and target. Staying within the confines of the sensor detection distance is something that the end user has to accomplish. Also, as noted before, the target has to pass over the sensor's sensing face within the detection distance to activate the sensor.
To better understand how the sensor operates, we will use an example, such as a common lead pencil. The pencil resembles an inductive proximity sensor because it is tubular in design and has an eraser on one end which also resembles the sensing face of sensors. With that in mind, if a metal target is passed close to the eraser face, it becomes active or turns on. If the target passes perpendicularly or longitudinally over the body of the pencil but not coming within the detection distance of the eraser or face, it will not turn on. The target metal also must be within the detection distance of the face or, as in the example, eraser before sensor turns on.